Integrated circuit chip produced by using frequency doubling hybrid photoresist

ABSTRACT

A photoresist composition is disclosed having both negative tone and positive tone responses, giving rise to spaces being formed in the areas of diffraction which are exposed to intermediate amounts of radiation energy. This resist material may be used to print doughnut shapes or may be subjected to a second masking step, to print lines. Additionally, larger and smaller features may be obtained using a gray-scale filter in the reticle, to create larger areas of intermediate exposure areas.

RELATED APPLICATIONS

This application is a division of the earlier patent application byHakey et al. entitled “FREQUENCY DOUBLING HYBRID PHOTORESIST HAVINGNEGATIVE AND POSITIVE TONE COMPONENTS AND METHOD OF PREPARING THE SAME”,Ser. No. 08/715,287, filed Sep. 16, 1996 now U.S. Pat. No. 6,114,082,that is incorporated herein by reference. This application is a sisterapplication to co-pending U.S. Patent Application by Holmes et al.entitled “LOW ‘K’ FACTOR HYBRID PHOTORESIST”, Ser. No. 08/715,288, filedSep. 16, 1996, that is likewise incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to the manufacture of integratedcircuit (IC) chips, and more specifically, to a photoresist materialthat includes both positive tone and negative tone attributes.

2. Background Art

Manufacturing of semiconductor devices is dependent upon the accuratereplication of computer aided design (CAD) generated patterns onto thesurface of a device substrate. The replication process is typicallyperformed using lithographic processes followed by a variety ofsubtractive (etch) and additive (deposition) processes.

Photolithography, a type of lithographic process, is used in themanufacturing of semiconductor devices, integrated optics, andphotomasks. The process basically comprises: applying a layer of amaterial that will react when exposed to light, known as a photoresistor, simply, a resist; selectively exposing portions of the photoresistto light or other ionizing radiation, i.e., ultraviolet, electron beams,X-rays, etc., thereby changing the solubility of portions of thematerial; and developing the resist by washing it with a basic developersolution, such as tetramethylammonium hydroxide (TMAH), thereby removingthe non-irradiated (in a negative resist) or irradiated (in a positiveresist) portions of the layer.

Conventional positive and negative tone photoresists are characterizedby a dissolution curve in which there is a single transition from afirst dissolution rate to a second dissolution rate as the resist isexposed to varying levels of actinic radiation. In a positive resist,the initially unexposed resist is insoluble in developer, while theexposed resist becomes more soluble as the exposure dose is increasedabove a threshold value. For a negative resist, similar behavior isobserved, except that the initially unexposed resist is soluble indeveloper, and the exposed area is rendered insoluble. By means of thisdifferential solubility between the exposed and unexposed resist areas,it is possible to form a pattern in the resist film. This pattern can beused to form integrated circuit devices, and is currently a criticalcomponent in their manufacture.

In an ideal situation, the exposure tool would only allow the radiationto hit the resist material in the areas of the mask that are clear, thusproviding sharp edges for the lines and spaces. However, diffractionpatterns are formed at the edges of the clear areas, resulting inpartial exposure of the resist in those areas. Certain patents havetaken advantage of this phenomenon, such as U.S. Pat. No. 4,568,631issued to Badami et al. on Feb. 4, 1986 and assigned to the assignee ofrecord for the present invention, which discloses utilizing a positiveresist and an additive for image reversal in order to create thin resistlines only in the areas where light intensity has been reduced bydiffraction effects. However, this procedure uses a resist withconventional positive and negative tone dissolution responses andrequires two separate expose and develop operations to form a resistimage from the edge of a reticle image.

As the need for higher and higher levels of integration has arisen inthe industry, the need for a larger number of lines and spaces in agiven area has increased dramatically. In response, a primary subject ofresearch has been enhancement of the exposure tool and reticle system toenhance the aerial image of the circuit pattern. For example, phaseshift reticles, shorter wavelength expose tools, higher numericalaperture expose tools, and tools with selective illumination systems arecontinuing to be developed to improve the pattern density of integratedcircuits. Due to the high cost, poor yield, and difficulty of inspectionand repair, phase shift reticles are generally not available for use.Due to the complexity of exposure tool design and construction, it isvery expensive to build higher numerical aperture and shorter wavelengthexpose systems.

In another area of activity, efforts are being made to improve thecontrast of the photoresist. However, the basic mechanism of operationof the photoresist continues to be the same; that is, the resists behaveas either positive or negative tone systems. It is desirable, therefore,to devise new mechanisms of resist response such that conventionaloptical lithography can be extended to smaller feature sizes withoutdeveloping new tools and reticles. Additionally, as these new tools andreticles are eventually developed and implemented, these new resistapproaches would remain applicable as a further extension oflithographic capability.

Presently, for high performance devices, the control of the image sizeon the reticle and the control of image size from one batch of wafers tothe next comprise the largest contributors to image size variation onthe product. Chip yield at high performance is strongly dependent on theuniformity of the image pattern across the chip and the centering of theimage pattern at the correct dimension. These limitations existcurrently for all types of lithographic patterning which use a reticle;optical, x-ray, and proximity E-beam, for example. The problem of imageuniformity across the reticle is especially acute for lithographictechniques that use 1× masks, such as x-ray and proximity E-beamlithography. It is therefore desired to provide a photoresist materialthat allows very precise image control for the image size, independentof the image size control on the reticle.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a photoresist materialhaving, simultaneously, both a positive tone and a negative toneresponse to exposure. This combination of materials can provide a newtype of resist, which we call a hybrid resist.

As a hybrid resist is exposed with actinic radiation, areas exposed withhigh intensity radiation form a negative tone line image. Areas whichare unexposed remain insoluble in developer, thus forming a positivetone line pattern. Areas which are exposed with intermediate amounts ofintensity, such as the edges of the aerial image where diffractioneffects have reduced the intensity, form a space in the resist filmduring develop. This resist response is an expression of the uniquedissolution rate properties of this resist, in which unexposed resistdoes not develop, partially exposed resist develops at a high rate, andhighly exposed resist does not develop.

It is, therefore, a feature of the present invention that the uniquedissolution rate response of the hybrid photoresist allows a singleaerial image to be printed as a space/line/space combination rather thanas a single line or space, as with conventional resist. This ‘frequencydoubling’ capability of this resist allows conventional expose systemsto be extended to higher pattern densities. It is an advantage of oneexample of the present invention that lines and spaces of 0.2 μm andless can be printed with current deep ultra violet (DUV) lithographytools that are designed for operation at 0.35 μm resolution.

It is a further advantage of this type of hybrid resist that the spacewidth is generally unchanging as the exposure dose and the reticle imagesize are changed. This allows very precise image control for the spacewidth within each chip, across each wafer, and from one batch of productwafers to the next.

Still another advantage of this invention is the relaxation of theminimum reticle feature size due to the frequency doubling capability ofhybrid resist. For example, to print a 0.2 μm feature with conventionalresist generally requires a 0.2 μm reticle image size. With hybridresist, a 0.2 μm space can be formed with a single edge of a reticlefeature; for example, a 0.5 μm reticle opening could produce two 0.2 μmspaces and a 0.2 μm line. In this way, one could accomplish ‘reduction’x-ray or E-beam lithography; the reticle image pitch could beapproximately 2× the printed pitch on the substrate. This also has theadditional advantage of allowing a relaxation of the image sizerequirements of optical reticles, reducing cost and improving yield ofthe reticle.

It is an advantage of the present invention that lines and spaces of 0.2μm and less may be achieved without altering the present tools.

It is a further advantage that the space width is generally unchangingas the exposure dose and reticle sizes change, thereby allowing greaterprocess latitude for control of space width. Through the use of thehybrid resist of the present invention, errors in the image dimension onthe reticle are not reproduced in the space width printed on thesubstrate. As a result, the across-chip space width variation isminimized. This is valuable for optical, X-ray and e-beam exposuremethods. It is especially useful in lithographic techniques that requirea 1× reticle, i.e., a reticle that normally has a one-to-onerelationship with the image printed on the substrate, because variationsin the image size on the reticle are normally reproduced on thesubstrate.

The foregoing and other features and advantages of the invention will beapparent from the following more particular description of preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawings will be provided by the Patentand Trademark Office upon request and payment of the necessary fee.

The preferred exemplary embodiment of the present invention willhereinafter be described in conjunction with the appended drawings,where like designations denote like elements, and:

FIG. 1 is a schematic of the use of the present invention;

FIG. 2 is a graph of linewidth in nanometers (nm) plotted against focusin microns (μm) of a formulation of a standard negative resist atvarious exposure energies;

FIG. 3 is a graph of linewidth for a negative tone line of a hybridpattern in nm plotted against focus in μm of a hybrid resist of thepresent invention at various exposure energies;

FIG. 4 is a graph showing the linewidth in nm plotted against the amountof positive tone solubility inhibitor (MOP) incorporated in a hybridresist of the present invention;

FIG. 5 is a comparative model of what the range of focus is for a givenlinewidth using standard resist formulations and a hybrid resistformulation of the present invention;

FIG. 6 is a graph showing the relationship between the cell area and thegeneration of the device;

FIG. 7 is a color schematic showing a sample layout for a six squarecell in which a hybrid resist of the present invention may be used toform the bitline;

FIG. 8 is a color schematic showing a sample layout for a four squarecell in which a hybrid resist of the present invention may be used toform the device;

FIG. 9 is a graph showing the dissolution rate in nanometers per second(nm/sec) as a function of the exposure dose in milliJoules (mJ) usingone formulation of a hybrid resist of the present;

FIG. 10 is a scanning electron micrograph of the lines and spaces formedusing one formulation of a hybrid resist of the present invention;

FIG. 11 is a graph showing the resultant line and space widths asfunctions of the chrome space width using one formulation of a hybridresist of the present invention;

FIG. 12 is a graph showing the dissolution rate of an alternativeformulation of the hybrid resist in nm/sec as a function of the exposuredose in mJ;

FIG. 13 is a graph showing the variation in space width in μm as afunction of MOP loading using one formulation of hybrid resist of thepresent invention;

FIG. 14 is a graph of the response of a formulation of the hybrid resistof the present invention in which exposed (negative) line, unexposed(positive) line and space widths are plotted as a function of exposuredose;

FIG. 15 is a scanning electron micrograph of 0.18 μm resist lines andspaces printed on a 0.5 numerical aperture (NA) deep ultra violet (DUV)expose tool with a hybrid resist formulation as described in Example 2of the present invention;

FIG. 16 is a graph showing dissolution rate as a function of exposuredose for a positive photoresist;

FIG. 17 is a graph showing image height as a function of dimension for apositive photoresist;

FIG. 18 is a graph showing dissolution rate as a function of exposuredose for a negative photoresist;

FIG. 19 is a graph showing image height as a function of dimension for anegative photoresist;

FIG. 20 is a graph showing dissolution rate as a function of exposuredose for a hybrid photoresist of the present invention; and

FIG. 21 is a graph showing image height as a function of dimension for ahybrid photoresist of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Accordingly, the present invention provides a photoresist materialhaving, simultaneously, both a positive tone and a negative toneresponse to exposure. The positive tone response dominates at the lowerexposure dose while the negative response predominates at the higherexposure dosages. Exposure of this resist creates a space/line/spacecombination, whereas either of the conventional resists would produceonly a single feature. Turning to FIG. 16, a graph is illustratedshowing how the positive resist undergoes an increase in solubility asthe exposure dose is increased. Turning to FIG. 17, the line pattern forpositive resist is illustrated. On the other hand, in the negativeresist system exposed areas undergo a reduction in solubility as theexposure dose is increased as illustrated in FIG. 18. Turning to FIG.19, the line pattern for negative resist printed with a reticle linepattern is illustrated. For the hybrid resist of the present invention,the positive tone response causes an increase in solubility in the areaswhere diffraction effects have reduced the expose intensity, such as theareas near the edge of the reticle image. As the exposure dose isincreased, the negative tone response predominates, causing a reductionin solubility in the more highly exposed areas. Turning to FIG. 20, thegraph of the resist solubility as a function of exposure dose for hybridresist is illustrated. Printing a reticle line pattern onto a substrateresults in the space/line/space pattern illustrated in FIG. 21. In thismanner, the aerial image is “frequency doubled” to produce twice thenumber of features than would otherwise be attainable with the standardresist. FIG. 1 illustrates these salient differences between a positiveresist, a negative resist, and a hybrid resist.

The frequency doubling hybrid resist is typically formulated usingcomponents of existing positive and negative tone resists. Thisincludes, for example, poly(hydroxystyrene) resins which are partiallymodified with acid-sensitive solubility dissolution inhibitingfunctionalities, a cross-linker, a photo-acid generator, and,optionally, a base additive and a photosensitizer.

The resist formulations may be varied to obtain a fast positive tonereaction and a slow negative tone reaction for optimal results.Additionally, the positive tone component can be chosen such that it isrelatively insensitive to post expose bake temperatures, while thenegative tone portion is chosen to be more highly sensitive to postexpose bake temperatures. In this way, the relative sensitivity of thepositive and negative responses can be altered with bake temperatures toprovide the desired imaging results.

In addition, the resist formulations may be altered to provide spacewidths of different dimensions. For example, as the amount of solubilityinhibitor on the poly(hydroxystyrene) resin is increased, the printedspace width becomes smaller (FIG. 13). This approach may also be used toalter the isofocal print bias of the negative tone line; at higherpositive tone solubility inhibitor concentrations, the isofocal printbias of the negative tone line increases (FIG. 4). This is desirable insome applications for reducing the size of the printed negative toneline, optimizing the frequency doubling characteristics of the resist.

The relative responses of the positive and negative tone functions ofthe hybrid resist can also be altered by modifying the exposureconditions. For example, the negative tone line of the hybrid resistdoes vary with exposure dose and reticle dimension, similar to thebehavior of a conventional resist. Thus, as exposure dose is increased,for example, the negative tone line increases in width, and the spacesremain the same size, but the spaces are shifted to a new position onthe substrate, since they lie adjacent to the negative line. Similarly,the positive tone lines alter in size as the exposure dose or reticledimension are altered.

As another example, two reticles could be used to print two separatepatterns in the resist. One reticle could be exposed with a high dose,causing the hybrid functions to be expressed in the resist. Anotherreticle could be exposed in the same resist film at a lower dose,causing only the positive tone function to be expressed in that portionof the resist. This effect could also be accomplished with a singleexpose process if, for example, the reticle contained a partial filterof the actinic radiation in the areas where a lower exposure dose wasdesired. This allows wider spaces to be printed at the same time as thenarrower features, which is necessary in some device applications.

In a modification of this two-step imaging approach, a hybrid resist canbe used to create a standard negative tone pattern. If the resist filmis image-wise exposed with a standard negative tone reticle, baked toform the hybrid image, then blanket exposed with actinic radiation anddeveloped without a second post-expose bake process, the result is astandard negative tone image. This approach may be desirable in someapplications, such as the formation of gate conductor circuits, whichrequire very small lines to be printed, but do not require a highdensity image pitch. As an alternative to this method, the resist may beblanket exposed to a low dose of actinic energy after the image-wiseexposure and before the baking step. The desirability of the methodwould depend on whether a solubility inhibiting protective group ispresent on the resin and whether the positive tone response istemperature dependent.

An advantage of using the hybrid resist in such application is that thenegative tone line of the hybrid resist can exhibit a large print biasat its isofocal point, as shown in FIG. 3. In other words, at the pointof largest process latitude for the hybrid negative tone line, theresist image size can be substantially smaller than the reticle imagesize. This is desirable because the aerial image is less degraded bydiffraction effects at the larger reticle size, thus allowing a largerdepth of focus to be attained than is possible with conventionalpositive and negative tone systems, as shown in FIG. 2. This print biasis a result of the fact that the edge of the chrome line prints as aspace. The space, in effect, acts to ‘trim’ the edges of the aerialimage, causing the negative line to print smaller than it would with aconventional negative resist. This is an expression of the frequencydoubling character of a hybrid resist.

It is possible to design the resist formulation to optimize the printbias of the negative tone line. For example, by choosing an appropriateloading factor for the positive tone solubility inhibitor, one mayobtain a particular print bias as shown in FIG. 4. In theory, it isquite obvious that similar variations in the photoresist response canalso be brought about by making appropriate changes in concentrationsand reactivities of other components as well.

For example, we have found that with exposure on a DUV 0.5 NAlithography tool, the isofocal print bias for a hybrid resist can be0.11 μm larger than the isofocal print bias for a standard negative toneresist, as exemplified in FIGS. 2 and 3 when standard calculations knownin the art are performed on the data. This difference can be utilized intwo ways. In one approach, the same reticle image size could be usedwith the hybrid resist to print a smaller line than the standard resist,while maintaining focus and exposure process latitude. In another mannerof use, the size of the reticle features could be increased with thehybrid resist relative to the standard resist, while printing the sameimage size as the standard resist. The use of a larger reticle imageprovides a larger depth of focus due to reduced diffraction effects, asshown in the graph of FIG. 5. In the former application, higherperformance is achieved with the smaller size of the hybrid resist. Inthe latter application, higher yield is achieved due to the largerprocess latitude of the hybrid resist.

The resist formulations may be varied to obtain a high photospeedpositive tone reaction and a low photospeed negative tone reaction foroptimal results. Additionally, the positive tone resist may be chosen sothat it is insensitive to post expose bake (PEB) conditions so that theratio of sensitivity of the positive tone to the negative tone functioncan be altered, thus changing the ratios of the space/line/spacecombinations.

Another option for changing the space/line/space ratios is to utilize agray-scale filter in the reticle of the exposure tool. A gray scalefilter only allows a portion of the radiation to pass through thereticle, thereby creating areas of intermediate exposure. This preventsthe negative tone resist function from operating in these areas becausethe exposure dose would never reach the critical point, but would stillallow the positive functions to occur, thereby creating wider spaces.This allows wider spaces to be printed at the same time as the narrowerfeatures, which is necessary in some device applications.

In a further processing refinement, the doughnut shaped features thatare typically obtained can be trimmed with a second masking step if theyare not desired. Although circular or oblong doughnut-shaped trenchesare desirable in deep trench capacitors in dynamic random access memory(DRAM) and first level wiring of the 1 gigabyte(GB) DRAM, lines arenecessary for the four square (4 SQ) and six square (6 SQ) wiring ofbitlines and wordlines. As shown in FIG. 6, the trends in cell area pergeneration show that the typical eight square (8 SQ) line is not goingto meet the area requirements for the 1 GB and higher density devices.For this reason, changes in device layout, such as staggered bitlines,have been suggested. However, with the reliable, sub-lithographicfeatures, as disclosed in the present invention, the folded bitlinearchitecture of the chip would still be possible. Additionally, shouldfurther advances be made in the device layout, the ability to reduce thefeature size may enhance the device's overall performance and size.

As shown in FIG. 7, a 6 SQ stacked capacitor folded bitline architectureis provided in which the pitch of the bitline is 1.5 F, as is requiredin order to make the appropriate connections. By reducing the pitch ofthe bitlines even further to 1.0 F and reducing the width of the shallowtrench isolation (STI) level in the vertical direction, a 4 SQ stackedcapacitor folded bitline architecture is attainable with the currenttechnology as shown in FIG. 8. For the 4 SQ, the stacked capacitors inthe y-direction will also have to be defined using the hybrid resist ofthe present invention.

The following examples are exemplary of the frequency doubling resistcomposition, but are not meant to be limiting and many variations willbe readily apparent to one of ordinary skill in the art.

The photoresist resins suitable for use in accordance with the inventioninclude any of the base-soluble, long chain polymers suitable for use asa polymer resin in a photoresist formulation. Specific examples include:(i) aromatic polymers having an —OH group, e.g., polyhydroxystyrenessuch as poly (4-hydroxystyrene), poly (3-hydroxystyrene), commerciallyavailable from Hoechst Celanese of Corpus Christi, Tex., novolak resinscommercially available from Shipley of Marlboro, Mass., and polymershaving a phenolic —OH group, e.g., phenol formaldehyde resins; (ii)polymers having an acid group, e.g., polymethacrylic acid with an esterside chain; and (iii) acrylamide group type polymers.

The polymer resin in its deprotected form, i.e., once the positive tonereaction has occurred is base base soluble and compatible with developersolutions, such as aqueous solutions of metal-free ammonium hydroxide,tetramethylammonium hydroxide, and tetraethyl ammonium hydroxide, metalcontaining potassium hydroxide, and sodium metasilicate. Preferredpolymer resins have an average molecular weight within the range ofabout 1,000 daltons to about 250,000 daltons, and most preferably withinthe range of about 1,000 to 25,000 daltons, to enhance its solubility indeveloper solutions. Examples include p-hydroxystyrene-maleic acidanhydride copolymers,polyhydroxystyrene-p-tertiarybutyl-carganatostyrene co-polymers,poly(2-hydroxystyrene), phenol-formaldehyde resins, polymethylmethacrylate-tertiary butyl methacrylate-polymethacrylic acidterpolymers, poly-4-hydroxystyrene-tertiary butyl methacrylatecopolymers, poly(4-hydroxystyrene) with one or more acid labile alkyl oraryl substituents on the aromatic ring, a poly(3-hydroxystyrene) withone or more alkyl or aryl substituents on the aromatic ring, or any ofthese as the major number of subunits in a copolymer, such as PHM-C,commercially available from Maruzen America of New York, N.Y. The PHM-Cincludes both poly (hydroxystyrene) subunits and vinyl cyclohexanolsubunits preferably being in the range of about 99:1 to about 50:50. Themost preferred ratio is about 90 poly (hydroxystyrene) units to about 10vinyl cyclohexanol subunits.

Crosslinking compositions are preferably tetramethoxymethyl glycouril(“Powderlink”) and 2,6-bis(hydroxymethyl)-p-cresol. However, otherpossible crosslinking compositions include:

their analogs and derivatives, as can be found in Japanese Laid-OpenPatent Application (Kokai) No. 1-293339, as well as etherified aminoresins, for example methylated or butylated melamine resins(N-methoxymethyl- or N-butoxymethyl-melamine respectively) ormethylated/butylated glycol-urils, for example of the formula:

as can be found in Canadian Patent No. 1 204 547.

Photoacid generators (“PAG”) include, but are not limited to:N-(trifluoromethylsulfonyloxy)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide(“MDT”), onium salts, aromatic diazonium salts, sulfonium salts,diaryliodonium salts and sulfonic acid esters of N-hydroxyamides or-imides, as disclosed in U.S. Pat. No. 4,731,605, incorporated herein byreference. Also, a PAG that produces a weaker acid such as dodecanesulfonate of N-hydroxy-naphthalimide (“DDSN”) may be used.

Possible base additives include, but are not limited to: dimethylaminopyridine, 7-diethylamino-4-methyl coumarin (“Coumarin 1”), tertiaryamines, proton sponge, berberine, and the polymeric amines as in the“Pluronic” or “Tetronic” series from BASF. Additionally, tetra alkylammonium hydroxides or cetyltrimethyl ammonium hydroxide, may be usedwhen the PAG is an onium salt.

Examples of sensitizers that may be utilized include: chrysenes,pyrenes, fluoranthenes, anthrones, benzophenones, thioxanthones, andanthracenes, such as 9-anthracene methanol (9-AM). Additional anthracenederivative sensitizers are disclosed in U.S. Pat. No. 4,371,605, whichis incorporated herein by reference. The sensitizer may include oxygenor sulfur. The preferred sensitizers will be nitrogen free, because thepresence of nitrogen, e.g., an amine or phenothiazine group, tends tosequester the free acid generated during the exposure process and theformulation will lose photosensitivity.

The casting solvent is used to provide proper consistency to the entirecomposition so that it may be applied to the substrate surface withoutthe layer being too thick or too thin. Sample casting solvents include:ethoxyethylpropionate (“EEP”), a combination of EEP and γ-butyrolactone(“GBL”), and propylene-glycolmonoethylether acetate (PM acetate).

In the following Examples, one of each of these has been chosen,however, it is to be recognized that many other compositions may beselected for various portions of the resist, the basis of the inventionlies in the fact that the hybrid resist is comprised of a negative tonecomponent and a positive tone component, wherein the positive tonecomponent acts at a first actinic energy level and the negative tonecomponent acts at a second actinic energy level, the first and secondactinic energy levels being separated by an intermediate range ofactinic energy levels.

EXAMPLE 1

The following compositions were dissolved in propylene-glycolmonomethylether acetate (PM acetate) solvent available from Pacific Pac,Inc., Hollister, Calif. containing 350 ppm of FC-430, a non-ionicfluorinated alkyl ester surfactant available from 3M, St. Paul, Minn.for a total of 20% solids:

poly(hydroxystyrene) (PHS), 10% hydrogenated, available from MaruzenAmerica, New York, N.Y. with about 25% of the phenol groups protectedwith methoxypropene (MOP), 81.2% of solids;

N-(trifluoromethylsulfonyloxy)-bicyclo-[2.2.1]-hept-5-ene-2,3-dicarboximide(MDT), available from Daychem Labs, Centerville, Ohio, 10.5% of solids;

tetramethoxymethyl glycouril (Powderlink), available from Cytec,Danbury, Conn., 8.2% of solids; and

7-diethylamino-4-methyl coumarin dye (Coumarin 1), available from theAldrich Chemical Company, 0.1% of solids.

The solution was filtered through a 0.2 μm filter. The solution wascoated onto silicon wafers primed with hexamethyl-disilazane with a softbake of 110° Celsius (C.) resulting in films of about 0.8 μm thick asdetermined by a Nanospec reflectance spectrophotometer. The coatedwafers were then exposed with deep ultraviolet (DUV) excimer laserradiation having a wavelength of 248 nm in a 0.37 numerical aperture(NA) Canon stepper with a matrix of different doses from low doses tohigh doses and post expose baked (PEB) at 110° C. for 90 sec. Thedissolution rates of the exposed films were calculated from thethickness of remaining film after developing for a given amount of timewith 0.14 Normal (N) tetramethylammonium hydroxide (TMAH) developer. Thedissolution rate vs. exposure dose relationship is shown in FIG. 9. Asshown in FIG. 9, the resist has a very low dissolution rate (about 2nm/sec) when unexposed. As the dose is increased, the dissolution rateincreases until reaching about 50 nm/sec. The dissolution rate remainsrelatively constant at this level in the dose range of about 1milliJoule (mJ) to about 3 mJ. Increasing the dose further, the negativecross-linking chemistry becomes predominant and the dissolution ratefalls back to a value close to zero.

A typical lithographic response of this resist is illustrated in FIG.10, which shows the outcome of exposing the resist through a mask having1 μm wide nested chrome lines at a pitch of 2 μm with a 248 DUV stepperwith a 0.37 NA. Every chrome line and space combination in the maskprints as two lines and two spaces on the resist: a negative line ofabout 0.8 μm, a positive tone line of about 0.6 μm and two equal spacesof about 0.3 μm.

In another experiment with the same resist, when a MICRASCAN II 0.5 NADUV stepper is used to expose an isolated chrome space onto the hybridresist film, the space/line/space measurements as a function of width ofthe chrome space are plotted, as shown in FIG. 11. The data suggeststhat, although the width of the line increases correspondingly with thatof the chrome space on the mask, the space on either side of the lineremains relatively constant.

EXAMPLE 2

This example illustrates the manner in which changing the type ofphotoacid generator and relative amounts of the various components canchange the dissolution rate characteristics of the hybrid resist andsubsequently the lithographic response. This second formulation wasprepared and processed in a manner similar to EXAMPLE 1, however, it iscomprised of the following components:

PHS with about 25% of the phenol groups protected with MOP, 90.8% ofsolids;

triphenyl sulfonium triflate, 1.3% of solids;

Powderlink, 7.8% of solids;

tetrabutyl ammonium hydroxide base, 0.1% of solids; and

sufficient PM acetate containing 350 ppm FC-430 surfactant as a solventto form a 18.9% solids solution.

The dissolution rate characteristic of the resulting hybrid resist isshown in FIG. 12. The overall nature of the curve remains similar tothat shown by the hybrid resist of EXAMPLE 1, in that the dissolutionrate starts out low for an unexposed resist, increases to a high atabout 5 mJ and decreases to a low above 7 mJ. However, the absolute doserange and the dissolution rates within these ranges are quite differentfrom those shown in FIG. 9.

FIG. 14 represents the response of this formulation of the hybrid resistwhen exposed through a mask of nested chrome lines and spaces of equalwidths in a MICRASCAN II DUV 0.5 NA stepper tool. Negative line,unexposed (positive) line and space widths are plotted as a function ofmask dimension. The space remains relatively constant in the range ofabout 0.18 μm, whereas both lines vary as the mask dimension is varied.Resist images representative of this formulation and process are shownin FIG. 15.

EXAMPLE 3

This example illustrates that the space width of the frequency doubledimage can be changed by varying the protection level of PHS with MOP.Two different PHS lots having 24% and 15% MOP loading, respectively,were used to make hybrid formulations identical to that of EXAMPLE 1,except that the total solids contents were adjusted to 16.0% of thetotal to obtain film thicknesses of about 0.5 μm. From these two stockformulations, several other formulations with average MOP levels rangingfrom 15 to 24% were prepared. Wafers were coated and soft baked at 110°C., exposed on a MICRASCAN II DUV 0.5 NA stepper, post exposed baked at110° C. for 60 sec and finally developed with 0.14N TMAH developer. Areticle with an isolated chrome opening was printed in a hybrid resistfilm. The spacewidth of the resist image was measured and graphed as afunction of the average MOP solubility inhibitor loading in the PHS usedfor making the respective formulations. It was found that the spacewidth was strongly dependent on MOP concentration, as shown in FIG. 13.

EXAMPLE 4

Negative tone imaging may be performed with the hybrid resist of thepresent invention, using a blanket DUV expose after the PEB and prior tothe develop.

A hybrid resist formulation as described in EXAMPLE 2, above, wasimage-wise exposed with a chrome reticle with an electrical test patternon a 0.5NA DUV expose system. Silicon wafers (200 mm) with a 2000Angstrom (Å) film of polysilicon were used as a substrate so that theresulting etched patterns of the resist image could be measured withelectrical probe techniques. After the post expose bake process, thewafers were cycled back into the expose tool (MICRASCAN II) and exposedat 10 mJ per square centimeter (cm²) with a clear glass reticle. A postexpose bake process was not performed after the second exposure. Thepurpose of the second exposure was to remove the initially unexposedresist from the wafer, leaving only a negative tone resist pattern afterdevelop.

The initial image-wise expose dose was 17-24 mJ/cm2, the post exposebake temperature was 110° C. for 90 sec and the develop time was 100 secin 0.14N TMAH. A standard negative tone resist was processed in asimilar fashion, with the omission of a blanket expose step as acontrol. The electrical data from this experiment is shown in FIGS. 2and 3. A large isofocal print bias of approximately 0.11 μm was observedfor the hybrid resist relative to the standard negative resist, ascalculated using standard methods known in the art.

While the invention has been particularly shown and described withreference to preferred exemplary embodiments thereof, it will beunderstood by those skilled in the art that the foregoing and otherchanges in form and details may be made therein without departing fromthe spirit and scope of the invention.

Accordingly, what is claimed is:
 1. An integrated circuit chip comprising a bitline architecture, the integrated circuit chip produced by the steps of: a) selecting a hybrid photoresist composition having a negative tone response and a positive tone response to exposure to actinic radiation, wherein the negative tone response predominates over the positive tone response at less than a first exposure dose D₁ and at greater than a second exposure dose D₂, wherein the positive tone response predominates over the negative tone response between D₁ and D₂, and wherein D₁ is less than D₂; b) depositing a layer of the selected photoresist material onto a surface, thereby forming a film; c) exposing first portions of the film to a dose less than D₁, second portions of the film to a range of intermediate doses D_(INT), such that D_(INT) is less than or equal to D₂ and D_(INT) is greater than or equal to D₁, and third portions of the film to a dose greater than D₂; and d) developing the film, wherein at least one line and at least one space are formed.
 2. The integrated circuit chip of claim 1, the method further comprising the step of baking the film after exposing and before developing the film.
 3. The integrated circuit chip of claim 2, the method further comprising the step of blanket exposing the film after the exposure step and before the baking step.
 4. The integrated circuit chip of claim 2, the method further comprising the step of blanket exposing the film after the baking step and before the developing step.
 5. The integrated circuit chip of claim 2, the method further comprising the step of image-wise exposing the film after the baking step and before the developing step.
 6. The integrated circuit chip of claim 11, wherein changes of the exposusre dose have no effect on the size of the at least one space.
 7. The integrated circuit chip of claim 1, the method further comprising selecting a reticle having a frequency of lines and spaces, wherein the frequency of the lines and spaces is doubled.
 8. The integrated circuit chip of claim 1, wherein post exposure bake increases the negative tone response more than the positive tone response.
 9. The integrated circuit chip of claim 1, wherein the positive tone response is faster than the negative tone response.
 10. The integrated circuit chip of claim 1, the method further comprising the step of selecting the positive tone component to be less sensitive than the negative tone component to post expose bake conditions.
 11. The integrated circuit chip of claim 1, wherein the step of selecting a hybrid photoresist composition further comprises selecting a solubility inhibitor such that a spacewidth decreases as the concentration of the solubility inhibitor increases.
 12. The integrated circuit chip of claim 1, the method further comprising a step of utilizing a gray-scale filter during the exposure step, thereby creating areas of intermediate exposure. 